To many, including Dale Steyn, it looked like Klaasen was batting on a different pitch. But even Klaasen said after the game it wasn't that easy. So how did he cruise on a pitch where everyone else seemed to be scraping?
To say Klaasen didn't struggle at all would be a lie. He was on 4 off 12 balls at one stage, but he navigated his path smartly. Apart from that, he also had a couple of other things going for him.
When he came out to bat, South Africa were in a spot of bother at 29 for 3 in the sixth over. But the silver lining was that Bhuvneshwar Kumar, the only Indian bowler who looked threatening on the night and picked up those three wickets, was already into his third over.
Klaasen showed the smarts to play out the remaining three balls of his over. Bhuvneshwar didn't bowl again until the 18th over, by when Klaasen had already ensured South Africa's victory.
Klaasen also benefited from having spent 20 overs behind the stumps in the first innings. That gave him a pretty good idea of how the pitch was playing. He knew the fast bowlers were to be dealt with carefully and the spinners were the ones to be attacked.
While the ball was doing all sorts of tricks for the seamers, there wasn't much turn available for the slow bowlers. That meant Yuzvendra Chahal and Axar Patel had to rely on the variation in speed. But once Klaasen had his eye in, scoring against spinners didn't prove to be difficult as he consistently hit them through the line.
After a slow start, Klaasen gave himself room against Chahal and lofted him over extra-cover for a one-bounce four. Two balls later he slog-swept him over deep midwicket for the first of his five sixes.
He did something similar against Axar as well. First, he gave himself room to punch him to the extra-cover boundary and then rocked back to deposit the next ball over deep midwicket. In between, he picked up a couple of fours off Harshal Patel in the 11th over.
Heinrich Klaasen raises his bat on getting to his half-century. BCCI
At the end of eight overs, South Africa were 36 for 3 and needed another 113 from 12 overs at a rate of 9.41. But Klaasen's onslaught brought the equation down to 60 required from eight overs at a comfortable 7.50 runs per over.
His best shot, arguably, still came against a seamer. In the 14th over, Hardik Pandya bowled one full to the off stump. It wasn't easy to get under it and find the elevation, but with a whip of the bottom hand, Klaasen sent it sailing over long-on. Two overs later, he killed the contest by hitting Chahal for two more sixes.
What Klaasen's innings also did was allow Bavuma to play the anchor's role. The two added 64 off 41 balls for the fourth wicket. Klaasen's contribution to that was 49.
Then Klaasen and David Miller forged 51 off 28 balls for the fifth wicket. There too Klaasen was the dominant partner, scoring 32 off 17 balls. Given the small target, those two stands were all South Africa needed.
This knock comes at a crucial juncture in Klaasen's career. Before Sunday, Klaasen last played international cricket at the 2021 T20 World Cup. Since then, he has been dropped from the ODI side, and earlier this year, he also lost his central contract. He wouldn't have played here either had Quinton de Kock not injured his wrist.
"It's a blessing from above that this innings came at this time for me in my career," Klaasen said after the game. "That puts me on the map ahead of international cricket." So hopefully this will just prolong my career a little bit longer. "